Field of the Invention
The invention relates to a pressure-sensitive adhesive layer-attached polarizing film having a polarizing film and a pressure-sensitive adhesive layer provided on the polarizing film. The present invention also relates to an image display, such as a liquid crystal display, an organic electroluminescence (EL) display, or a plasma display panel (PDP), produced using the pressure-sensitive adhesive layer-attached polarizing film.
Description of the Related Art
The image-forming system of liquid crystal displays or the like requires polarizing elements to be placed on both sides of a liquid crystal cell, and generally polarizing films are bonded thereto. When the polarizing films are bonded to a liquid crystal cell, pressure-sensitive adhesives are generally used. Bonding between a polarizing film and a liquid crystal cell is generally performed with a pressure-sensitive adhesive in order to reduce optical loss. In such a case, a pressure-sensitive adhesive layer-attached polarizing film including a polarizing film and a pressure-sensitive adhesive layer previously formed on one side of the polarizing film is generally used, because it has some advantages such as no need for a drying process to fix the polarizing film. In general, a release film is attached to the pressure-sensitive adhesive layer of the pressure-sensitive adhesive layer-attached polarizing film.
During the manufacture of a liquid crystal display, the pressure-sensitive adhesive layer-attached polarizing film is bonded to a liquid crystal cell. In this process, static electricity is generated when the release film is peeled off from the pressure-sensitive adhesive layer of the pressure-sensitive adhesive layer-attached polarizing film. The static electricity generated in this manner may affect the orientation of the liquid crystal in the liquid crystal display to cause a failure. The static electricity may also cause display unevenness when the liquid crystal display operates. For example, the static generation can be suppressed when an antistatic layer is formed on the outer surface of the polarizing film, but its effect is not high, and there is a problem in which static generation cannot be fundamentally prevented. To suppress static generation in a fundamental position, therefore, the pressure-sensitive adhesive layer is required to have an antistatic function. Concerning means for providing an antistatic function to a pressure-sensitive adhesive layer, for example, it is proposed that an ionic compound should be added to a pressure-sensitive adhesive used to form a pressure-sensitive adhesive layer (Patent Documents 1 and 4). Concerning an acrylic pressure-sensitive adhesive for use in forming a polarizing film, Patent Document 1 discloses the addition of a lithium salt to such an adhesive, Patent Document 2 the addition of at least one of an alkali metal salt and an alkaline-earth metal salt to such an adhesive, Patent Document 3 the addition of an ionic compound having an organic cation and being solid at room temperature to such an adhesive, and Patent Document 4 the addition of an ionic solid containing an imidazolium cation and an inorganic anion to such an adhesive. There is also proposed a method of forming an antistatic layer between a polarizing film and a pressure-sensitive adhesive layer using a binder of a conductive polymer such as polythiophene. The pressure-sensitive adhesive layer-attached polarizing film is also required to have durability in the adhering state.
Patent Document 1: JP-A No. 2010-189489
Patent Document 2: JP-A No. 2010-065217
Patent Document 3: JP-A No. 2010-066756
Patent Document 4: JP-A No. 2009-251281
Patent Document 5: JP-A No. 2003-246874